Laminates

ABSTRACT

An adhesvie composition comprising a block copolymer produced by the polymerization of a conjugated diene and a hydrocarbyl-substituted styrene or the polymerization of a conjugated diene, styrene, and a hydrocarbyl-substituted styrene, the block copolymer having an inherent viscosity within the range of from about 0.5 to about 3. The compositions have utility in the formation of laminates from metals and other substrates.

This application is a divisional application of copending applicationhaving Ser. No. 813,583, filed July 7, 1977, U.S. Pat. No. 4,178,275,which in turn is a divisional application of our application having Ser.No. 636,488, filed Dec. 1, 1975, now abandoned, which in turn is acontinuation-in-part application of our application having Ser. No.141,996, filed May 10, 1971, now abandoned.

This invention relates to adhesive formulation and laminates.

In one of its more specific aspects, this invention relates to the useof block copolymers of dienes and hydrocarbyl-substituted styrenes asadhesives which have utility in the formation of laminates from metalsand other substrates.

The use of block copolymers, either linear or branched, in adhesivecompositions is well known. Such block copolymers are usually solidrubbery materials which are employed as a solution of the polymer in asuitable solvent vehicle.

According to this invention, there are provided adhesive formulationsemploying as the copolymer a block copolymer produced by thepolymerization of conjugated dienes and hydrocarbyl-substituted styrenesor mixtures thereof with styrene. These block copolymers are furthercharacterized as having high green strength, i.e., high tensile strengthin an uncured condition. The block copolymers of the invention can belinear or branched (radial) and can be represented by the generalformulas: (1) A--B--A and (2) (A--B)_(x) Z wherein A is a resinous(nonrubbery) polymer block (substituted styrene polymer block and,optionally, containing styrene) and B is a rubbery polymer block(conjugated diene polymer block) and wherein Z represents the residuefrom a coupling agent such as disclosed in U.S. Pat. No. 3,281,383 whichis capable of coupling two or more (A--B--) polymer blocks together andwherein x represents the number of (A--B--) polymer blocks thus coupledand is at least two and can be equal to the number of functional groupsin the coupling agent. It can be seen that if x in formula (2) above isgreater than two, a branched block copolymer results, while if x is 2, alinear block copolymer is formed. Formula (1) also represents a linearblock copolymer. It can also be noted that the above block copolymershave at least two terminal blocks per molecule that are resinous(nonrubbery) in nature. The resulting adhesive possesses high greenstrength, high tack, good film quality, and the formulation exhibits alow viscosity.

The conjugated dienes which can be used to produce the block copolymersare those having 4 to 12, and preferably 4 to 8, carbon atoms permolecule and are such as are disclosed in the prior art including1,3-butadiene, isoprene, 1,3-pentadiene, 1,3-octadiene, 1,3-dodecadiene,2-methyl-1,3-hexadiene, and the like.

The hydrocarbyl-substituted styrenes employable can be represented bythe general formula ##STR1## wherein n is an integer having a valuewithin the range of 1 to 5 and wherein R is a hydrocarbyl radicalcontaining from 1 to 12, preferably 3 to 8, carbon atoms. It ispreferred that the total number of carbon atoms in the substituent Rgroup, or R groups, be not greater than about 12. R is selected from thegroup consisting of alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, andcombinations thereof such as cycloalkyl or aralkyl, and the like. When Ris alkenyl or cycloalkenyl or combinations thereof, such unsaturatedsubstituents are of the nonpolymerizable type at polymerizationconditions employed in producing the block copolymers concerned.

Examples of suitable hydrocarbyl-substituted styrenes include4-methylstyrene, 3-ethylstyrene, 2,3,4,5,6-pentamethylstyrene,4-tert-butylstyrene, 2,4,6-triethylstyrene, 4-cyclopentylstyrene,4-(1-methylcyclohexyl)styrene, 4-n-dodecylstyrene,4-(4-n-octenyl)styrene, 3,5-di(2-cyclopentenyl)styrene,4-(2-ethyl-2-hexyl)styrene, 3-(2-methyl-2-butyl)styrene,4-phenylstyrene, 3-(4-cyclobutyl-1-octyl)styrene, 2,6-diethylstyrene,and the like.

It is to be understood that mixtures of hydrocarbyl-substituted styreneswith styrene can be employed in the method of this invention. It is alsoto be understood that mixtures of hydrocarbyl-substituted styrenes canbe employed and that such mixtures can include styrene. When mixtures ofthe hydrocarbyl-substituted styrenes with styrene are employed in theproduction of the block polymers, or if the hydrocarbyl-substitutedstyrene is used alone, the total amount of hydrocarbyl-substitutedstyrenes employed is in the range of from about 1 to about 20,preferably 2 to 7, parts by weight per hundred parts by weight of thetotal monomers, including diene content, which are employed, and theweight ratio of conjugated diene monomer to hydrocarbyl-substitutedstyrene or mixture thereof with styrene, is from about 50 to 50 to about90 to 10, and preferably from about 65 to 35 to about 85 to 15. Thus,based upon 100 percent conversion and 100 parts by weight of copolymer,the resulting copolymer contains from about 50 to about 90 parts byweight of conjugated diene and from about 50 to about 10 parts by weightof styrene and hydrocarbyl-substituted styrene. In view of theabove-described ranges for the hydrocarbyl-substituted styrene contentand the conjugated diene monomer content, it is readily apparent thatfor the embodiment wherein hydrocarbyl-substituted styrene(s) are usedalone, i.e., no styrene in admixture therewith, the ratio of conjugateddiene monomer to said hydrocarbyl-substituted styrene(s) is from 80/20to 90/10 for such block copolymers. However, for the embodiment whereina mixture of styrene and hydrocarbyl-substituted styrene is employed, itis apparent that a large number of block copolymer compositions areencompassed within said ranges of hydrocarbyl-substituted styrenecontent and conjugated diene monomer content. For example:

    ______________________________________                                        Diene/Styrene/Hydrocarbyl-substituted Styrene                                 ______________________________________                                        50        49      1                                                           50        30      20                                                          60        39      1                                                           60        20      20                                                          70        29      1                                                           70        10      20                                                          80        19      1                                                           80        1       19                                                          90        9       1                                                           90        1       9                                                           ______________________________________                                    

If mixtures of the hydrocarbyl-substituted styrene and styrene areemployed, these monomers can be introduced into the polymerizationreaction mixture as a preformed mixture or each can be individuallyintroduced, the first-introduced being polymerized to any desired extentbefore the addition of those subsequently introduced.

The polymerization conditions at which the polymers of this inventionare formed, including temperature, pressure, reaction time,polymerization initiator levels, presence of inert hydrocarbon diluentsin the reaction mixture, and methods of recovery of the block polymerfrom the reaction mixtures, are those well known in the art. Forexample, radial block copolymers of the above type are presentlypreferred and can be prepared by the procedures disclosed in U.S. Pat.No. 3,281,383, and linear block copolymers can be prepared by theprocedures of U.S. Pat. No. 3,251,905.

The block copolymers suitable for use in this invention will have aninherent viscosity within the range of from about 0.5 to about 3 andpreferably from about 0.9 to about 2, as determined by that procedureset forth in U.S. Pat. No. 3,278,508. The block copolymers of thisinvention can be recovered from the polymerization reaction mixture bythe usual prior art procedures. For example, the polymers can berecovered by evaporation of the diluent, by precipitation of the polymerfrom solution with a non-solvent (coagulant), or by steam stripping thepolymerization reaction mixture.

Since it is well known that the inherent viscosity of the blockcopolymers is generally inversely proportional to the polymerizationinitiator level, one skilled in the art can readily determine the properinitiator level to employ for the preparation of block copolymers havinginherent viscosities within the ranges disclosed above.

As indicated in the U.S. patents cited above, the organolithiumcompounds are preferred as polymerization initiators for the preparationof the block copolymers useful in this invention.

It is preferred that the polymerization reaction be carried out in thepresence of an inert hydrocarbon diluent. Typical suitable diluentswould include n-butane, n-hexane, cyclohexane, cyclooctane, toluene,benzene, and the like. Mixtures of such compounds can also be employed.If desired, ethers or thioethers can also be employed as thepolymerization diluent alone or in admixture with the abovehydrocarbons. If ethers or thioethers are thus employed, reasonable careshould be exercised to see that the presence of these compounds does notprevent the formation of the block copolymers of this invention.Step-wise addition and polymerization of the various monomers employedis an effective procedure for forming the block copolymers when ethersor thioethers are present in the polymerization reaction mixture.Suitable ethers and thioethers would include diethyl ether,tetrahydrofuran, 1,4-dioxane, di-n-butyl sulfide, and the like.

The block copolymers of the instant invention are preferably employed inthe form of a solution of the polymer in a suitable solvent vehicle inwhich the total solids concentration will generally be within the rangeof from about 10 to about 35 percent by weight. These vehicles can be,for example, naphthas and toluene, or mixtures thereof. Tackifiers,antioxidants, plasticizers, fillers, and other materials which can beconjunctively employed in the adhesive formulations of this inventionare those well known in the art.

In accordance with one presently preferred embodiment of the invention,the adhesive composition consists essentially of (a) a linear orbranched (radial) block copolymer produced by the polymerization ofconjugated dienes and hydrocarbyl-substituted styrenes or mixturesthereof with styrene as above described and (b) a tackifier.

The adhesive compositions of this invention are of thepressure-sensitive type and as such generally are applied to a substratein the form of a solution, dispersion, or emulsion. The amount ofsolvent employed is usually sufficient to provide a solution ordispersion in which the total solids concentration is within the rangeof about 10 to about 35 percent by weight, although the amount ofsolvent employed will often depend upon the particular method ofapplying the adhesive to a substrate and can vary appreciably.

Any inert organic solvent can be used as a solvent in the adhesivecompositions of this invention. Paraffinic hydrocarbons such as pentane,hexane, heptane, octane, nonane, and the like can be used.Cycloparaffinic hydrocarbons such as methylcyclopentane, cyclohexane,methylcyclohexane, and the like can be used. Aromatic hydrocarbons suchas benzene, toluene, and xylene can be used. The preferred solvents arethe cycloparaffinic hydrocarbons or mixtures thereof or mixtures ofcycloparaffinic hydrocarbons with aromatic hydrocarbons. Commerciallyavailable solvent mixtures such as naphthas (precipitation grade) arealso preferred solvents for the formulation. In one preferredembodiment, the organic solvent is a mixture of naphtha and toluene.

The amount of solvent present in the adhesive compositions is generallysufficient to reduce the viscosity of the adhesive composition to apoint where it can easily be applied to the surface of the material tobe bonded. The viscosity of the adhesive composition can vary over awide range. For example, it can be very viscous, paste-like materialwhen it is used for such purposes as applying floor tile, wall tile, andthe like. On the other hand, the solvent level of the adhesivecomposition can reduce the viscosity to a very low level for applicationthrough spray guns, aerosol applicators, and the like. It will beobvious to those skilled in the art that the exact amount of solventadded to the adhesive composition will be regulated by the use for whichthe adhesive composition is formulated.

Component (b) of the pressure-sensitive adhesive compositions of thisinvention is a material known in the art as a tackifier. Thesetackifiers can be any of the resinous substances known for enhancingtack of adhesive compositions. Examples of suitable tackifiers for usein accordance with this invention are those alkyd resins prepared byesterifying monocarboxylic or polycarboxylic acids with polyhydricalcohols. Such tackifiers are well known in the art and are exemplifiedby rosin, rosin derivatives, polyterpene resins, thermoplastic phenolicresins, hydrogenated rosin esters of pentaerythritol, coumarone-indeneresins, and the like.

The amount of tackifier added to the adhesive compositions of thisinvention is generally in the range of 0.4 to 1.5 parts by weight of atackifier per one part by weight of block copolymer.

The following examples will serve to further delineate the nature ofadhesive formulations which can be prepared with the block polymers ofthis invention. It will be seen that these adhesive formulations haveunexpectedly low solution viscosities but high shear adhesion strengthfor the adhesive in comparison to formulations employing blockbutadiene/styrene copolymers of a similar type. The low solutionviscosity of the present formulations facilitates their being handled.The high shear adhesion strength is, of course, a most desirableproperty by such adhesive compositions.

EXAMPLE I

Radial block copolymers of butadiene with styrene or mixtures thereofwith 4-tert-butylstyrene were prepared employing n-butyllithium as aninitiator, a cyclohexane diluent, a temperature of about 70° C., areaction time of about 30 minutes during which the styrene andtert-butylstyrene were polymerized, and an additional reaction period ofabout 30 minutes after the addition of butadiene. Polymerization of"styrenes" was essentially complete before butadiene was added. Thepolymerization recipe consisted of 780 parts by weight of cyclohexane,about 0.05 part by weight of tetrahydrofuran and styrene,4-tert-butylstyrene and butadiene, and n-butyllithium, in the partsindicated below. Each run was terminated with 0.5 parts by weight ofEpoxol 9-5, an epoxidized linseed oil having about 6 oxirane groups permolecule of glycerol triester. After each run, an antioxidant wasintroduced into the reaction mixture, the reaction mixture wascoagulated, and the polymer was separated and dried. The properties ofthe polymers and the components used in their preparation were asfollows:

    ______________________________________                                              Sty-              But-                                                  Poly- rene,  4-tert-Butyl-                                                                            adiene,                                                                             Inherent                                                                             n-Butyl-                                 mer   parts  styrene, parts                                                                           parts Viscosity                                                                            lithium, mhm.sup.(a)                     ______________________________________                                        1     40      0         60    0.87   2.6                                      2*    30     10         60    0.86   2.6                                      3*    20     20         60    0.88   2.6                                      4*    30     10         60    1.02   2.2                                      5*    30     10         60    1.17   2.0                                      6*    35     5          60    1.03   2.2                                      ______________________________________                                         *Invention runs.                                                              .sup.(a) mhm  gram millimoles per 100 g of monomers(s).                  

These polymers were individually compounded into pressure-sensitiveadhesives employing the following recipe:

    ______________________________________                                        Component             Parts by Weight                                         ______________________________________                                        Polymer               100                                                     Tackifier             100                                                     Antioxidant           1                                                       Naphtha, precipitation grade                                                                        419                                                     Toluene               47                                                      ______________________________________                                    

The tackifier was pentaerythritol ester of hydrogenated rosin and theantioxidant was octadecyl ester of3(3,5-di-t-butyl-4-hydroxy)phenylpropionic acid.

The resulting adhesives had the following properties:

    ______________________________________                                                 Formula-   Probe     Shear Adhesion                                           tion Vis-  Tack,     Hours to                                        Polymer  cosity, cp g         Failure                                         ______________________________________                                        1        8,600      354       1.7                                             2*       122        0         0.1                                             3*       114        0         0.03                                            4*       280        0         1.6                                             5*       1,392      557       0.6                                             6*       1,120      37        5.7                                             ______________________________________                                         *Invention runs.                                                         

Viscosities in centipoises are by Brookfield Viscosimeter Model RVF at24° C. Probe tack was determined by Polyken Probe Tack Tester per J.Appl. Poly. Sci., 14, p. 2039 (1970). Shear adhesion is based upon thetime required at 90° C. for 1/16-inch slippage of the bond formed by onesq. inch overlap of an adhesive-coated Mylar film on a steel substrate,the shearing stress being applied by a two-pound weight being hung fromthe vertical one-inch wide strip of Mylar film and being attached at anangle of 178° to the substrate.

The above data illustrate that the adhesive compositions of thisinvention possess high shear adhesion strength and relatively lowformulation viscosities.

It is to be emphasized that while the above examples employed certainreagents in the preparation of the polymers, the polymers of thisinvention can be produced employing any of the diluents, initiators,antioxidants, coagulants, coupling agents, and the like conventionallyemployed in polymerization reactions of the type concerned.

EXAMPLE II

Radial block copolymers of 1,3-butadiene with mixtures of styrene and4-tert-butylstyrene were prepared in accordance with the generalprocedure outlined above to produce polymers which were individuallycompounded into the adhesive formulations as previously defined.Polymers 7-12 were prepared with 0.5 part and polymers 13-18 with 0.3part of Epoxol 9-5 terminating agent. The charge order and polymerrecovery procedures were essentially the same as those given in ExampleI except that the antioxidant was changed to2,6-di-tert-butyl-4-methylphenol. Test procedures were as previouslydefined. Tests on the resulting adhesives were as follows:

    __________________________________________________________________________           Parts per Hundred    Adhesive Properties                                           4-tert-                 Shear                                                 Butyl-     Inherent                                                                           Visc.,                                                                            Tack,                                                                             Adhesion                                  Polymer                                                                              Styrene                                                                            styrene                                                                            Butadiene                                                                           Viscosity                                                                          cp  g   Hrs.                                      __________________________________________________________________________     7 (Control)                                                                         30   0    70    1.26 Insol.                                                                            860 5.2                                        8     29   1    70    1.18 8,500                                                                             900 5.8                                        9     27   3    70    1.16 1,160                                                                             920 4.6                                       10     25   5    70    1.26 1,100                                                                             720 6.1                                       11     24   6    70    1.32 1,050                                                                             740 5.1                                       12     22   8    70    1.31   910                                                                             520 3.0                                       13 (Control)                                                                         30   0    70    1.36 Insol.                                                                            850 4.2                                       14     29   1    70    1.39 Insol.                                                                            910 9.6                                       15     27   3    70    1.25 1,580                                                                             850 9.7                                       16     25   5    70    1.38   950                                                                             820 9.0                                       17     24   6    70    1.25   740                                                                             860 3.6                                       18     22   8    70    1.29   570                                                                             670 2.2                                       __________________________________________________________________________

Due to the insolubility of polymers 7, 13, and 14 in the originalformulation, the amount of toluene in the formulation recipe wasdoubled.

The above data indicate suitability of the compositions of thisinvention when prepared from 4-tert-butylstyrene and styrene mixtures.The above results demonstrate that polymers of this invention provideadhesive formulations of greatly reduced viscosity, excellent tack, andimproved shear adhesion strength.

EXAMPLE III

Radial block copolymers of butadiene with styrene or 4-methylstyrene ora mixture thereof were prepared in accordance with the generalprocedures outlined above to produce polymers which were individuallycompounded into the adhesive formulations comparable to those previouslydefined. All copolymers had inherent viscosities within the range of1.25 to 1.75. Tests of the resulting adhesives were as follows:

    ______________________________________                                        Parts per Hundred  Adhesive Properties                                        Poly- Sty-   4-Methyl- Buta- Visc.,                                                                              Tack, Shear Ad-                            mer   rene   styrene   diene cp    g     hesion, Hrs.                         ______________________________________                                        19    30     0         70    98,000                                                                              690   2.7                                  (Con-                                                                         trol)                                                                         20    30     0         70    104,000                                                                             680   2.5                                  (Con-                                                                         trol)                                                                         21    29     1         70    110,000                                                                             700   2.0                                  22    27     3         70    20,400                                                                              740   2.6                                  23    25     5         70    20,800                                                                              680   2.8                                  24    20     10        70    3,700 640   4.1                                  25    10     20        70    1,720 630   4.6                                  26     0     30        70    1,050 320   4.2                                  (Con-                                                                         trol)                                                                         ______________________________________                                    

Test procedures were as previously defined. These data indicate thesuitability of 4-methylstyrene as a reactant in the preparation of theadhesives of this invention. The results above illustrate again thereduced viscosity and improved shear adhesion strength that can beobtained employing the block copolymers of this invention.

EXAMPLE IV

In a manner comparable to that previously defined, copolymers ofbutadiene, styrene, and 4-ethylstyrene were produced and compounded intoadhesive formulations having the following composition and properties:

    ______________________________________                                                           Adhesive Properties                                                                         Shear                                        Parts per Hundred                Ad-                                                                 Bu-                   he-                                     Sty-   4-Ethyl- ta-  Inh. Visc.,                                                                              Tack, sion,                            Polymer                                                                              rene   styrene  diene                                                                              Visc.                                                                              cp    g     Hrs.                             ______________________________________                                        27     30     10       60   1.05 300   0     1.8                              28     0      40       60   1.16 320   0     1.05                             (Control)                                                                     ______________________________________                                    

The above data indicate that that adhesive composition encompassed bythe scope of this invention possesses a reduced formulation viscosityand increased shear adhesion strength as compared with that formulationoutside the scope of this invention. Test procedures were as previouslydefined.

EXAMPLE V

Other runs were made employing the general procedures of Example I withtwo different initiator levels and the monomer composition of Polymer10. Each run was terminated with the stoichiometric amount (based on theamount of n-butyllithium initiator) of silicon tetrachloride. Thecopolymers thus prepared were individually compounded into the adhesiveformulation recipe shown in Example I. The properties were determined asbefore and the results are shown below for these polymers and theformulations.

    ______________________________________                                        n-Butyl-            Adhesive Properties                                               lithium, Inh.   Visc.,                                                                              Tack, Shear Adhesion,                           Polymer mhm      Visc.  cp    g     Hrs.                                      ______________________________________                                        29      1.6      1.86   7,350 690   35                                        30      1.8      1.54   1,620 630   22                                        ______________________________________                                    

The above data demonstrate the outstanding properties, particularly inrespect to shear adhesion, of the adhesive composition of thisinvention.

It is to be understood that while the polymers of this invention havebeen illustrated in formulations with certain defined solvents,tackifiers, and antioxidants, the polymers of this invention can beemployed with any solvents, tackifiers, antioxidants, and the like whichare conventionally employed in adhesive compositions.

EXAMPLE VI

Other runs were made employing the general procedures of Example I withdifferent initiator levels and a monomer composition of Polymer 7(Polymers 31-40) or Polymer 10 (Polymers 41-53). Different levels ofsilicon tetrachloride (SiCl₄) were employed in the termination of theruns. The amount of SiCl₄ employed was based on the amount ofn-butyllithium initiator employed and is expressed in terms relative tothe theoretical stoichiometric amount of SiCl₄ required to react withsaid initiator. The block copolymers thus prepared were individuallycompounded into the adhesive formulation recipe shown in Example I. Theproperties were determined as before and the results are shown below forthese polymers and the adhesive formulations.

    ______________________________________                                                        Adhesive Properties                                                         SiCl.sub.4                 Shear                                Poly- n-BuLi  % of          Viscosity,                                                                           Tack, Adhesion,                            mer   mhm     Theory  I.V..sup.(a)                                                                        cp     g     Hrs.                                 ______________________________________                                        31    2.0      60     1.13  10,800 680   8.0                                  32    2.0     80      1.32  11,000 770   1.6                                  33    2.0     100     1.34  15,500 810   8.0                                  34    2.0     120     1.24  10,000 740   6.5                                  35    2.0     140     1.22  22,000 800   8.0                                  36    2.2     60      1.20  4,150  720   4.5                                  37    2.2     80      1.40  9,200  700   13.0                                 38    2.2     100     1.29  3,900  750   7.6                                  39    2.2     120     1.28  4,950  750   5.7                                  40    2.2     140     1.02  8,200  860   8.0                                  41*   1.6     60      1.50  2,100  700   16                                   42*   1.6     80      1.82  4,800  720   28                                   43*   1.6     120     1.77  3,950  690   31                                   44*   1.6     140     1.80  5,160  660   33                                   45*   1.8     60      1.58  1,700  710   15                                   46*   1.8     80      1.49  1,380  650   17                                   47*   1.8     120     1.55  2,100  640   23                                   48*   1.8     140     1.44  1,290  710   15                                   49*   2.0     60      1.22  470    770   2.0                                  50*   2.0     80      1.47  1,050  760   11                                   51*   2.0     100     1.38  890    750   8                                    52*   2.0     120     1.42  1,000  800   7                                    53*   2.0     140     1.10  1,330  830   9.5                                  ______________________________________                                         .sup.(a) Inherent viscosity                                                   *Invention runs.                                                         

The above data demonstrate the outstanding properties of the adhesivecompositions of this invention, particularly the combination of goodtack with very low formulation viscosity and exceptionally good shearadhesion values.

We claim:
 1. A plurality of layers having between adjacent surfacesthereof as a bonding material therefor an adhesive compositioncomprising as the rubbery component a radial block copolymer produced bythe polymerization of a conjugated diene, styrene, and ahydrocarbyl-substituted styrene of the formula ##STR2## in which R is ahydrocarbyl radical containing 1 to 12 carbon atoms selected from thegroup consisting of alkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, andcombinations thereof and n is an integer having a value within the rangeof 1 to 5, said block copolymer having an inherent viscosity within therange of from about 0.5 to about 3, said conjugated diene containing 4to 12 carbon atoms per molecule, the weight ratio of conjugated diene tothe total weight of said styrene and hydrocarbyl-substituted styrenebeing within the range of from about 50 to 50 to about 90 to 10, and theratio of said hydrocarbyl-substituted styrene to the total of saidconjugated diene, styrene, and hydrocarbyl-substituted styrene beingwithin the range of from about 1 to about 20 parts by weight of saidhydrocarbyl-substituted styrene per 100 parts by weight of the total ofsaid conjugated diene, styrene, and hydrocarbyl-substituted styrene andfurther wherein said rubbery block copolymer can be represented by thegeneral formula (A--B)_(x) Z wherein A is a resinous (nonrubbery)polymer block and B is a rubbery polymer block and wherein Z representsthe residue from a coupling agent which is capable of coupling two ormore (A--B--) polymer blocks together and wherein x represents thenumber of (A--B--) polymer blocks thus coupled and is greater than two.2. The laminate of claim 1 in which said block copolymer contains4-tert-butylstyrene.
 3. The laminate of claim 1 in which said blockpolymer is produced by the polymerization of 60-70 parts by weightbutadiene, 20-35 parts by weight styrene, and 1-20 parts by weight4-tert-butylstyrene.
 4. The laminate of claim 1 in which said blockcopolymer contains 4-methylstyrene or 4-ethylstyrene.
 5. The laminate ofclaim 1 in which said block polymer is produced by the polymerization of70 parts by weight butadiene, 10-29 parts by weight styrene, and 1-20parts by weight 4-methylstyrene.
 6. A plurality of layers having betweenadjacent surfaces thereof as a bonding material therefor an adhesivecomposition which consists essentially of(a) branched rubbery blockcopolymer having an inherent viscosity within the range of from about0.5 to about 3 of(1) at least one conjugated diene having from 4-12carbon atoms per molecule, (2) at least one hydrocarbyl-substitutedstyrene of the formula ##STR3## in which R is a hydrocarbyl radicalcontaining 1 to 12 carbon atoms selected from the group consisting ofalkyl, cycloalkyl, aryl, alkenyl, cycloalkenyl, and combinations thereofand n is an integer having a value within the range of 1 to 5, and (3)styrene, wherein said block copolymer, based on 100 parts by weight ofcopolymer, contains from about 50 to about 90 parts by weight of saidconjugated diene and from about 50 to about 10 parts by weight of saidstyrene and said hydrocarbyl-substituted styrene, and the amount of saidhydrocarbyl-substituted styrene, based on the total of said conjugateddiene, styrene, and hydrocarbyl-substituted styrene, is within the rangeof from about 1 to about 20 parts by weight of saidhydrocarbyl-substituted styrene per 100 parts by weight of the total ofsaid conjugated diene, styrene, and hydrocarbyl-substituted styrene, andfurther wherein said rubbery block copolymer can be represented by thegeneral formula (A--B)_(x) Z wherein A is a resinous (nonrubbery)polymer block and B is a rubbery polymer block and wherein Z representsthe residue from a coupling agent which is capable of coupling two ormore (A--B--) polymer blocks together and wherein x represents thenumber of (A--B--) polymer blocks thus coupled and is greater than two,and (b) from 0.4 to 1.5 parts by weight of a tackifier per one part byweight of said rubbery block copolymer and wherein in said adhesivecomposition said rubbery block copolymer is the sole rubbery polymertherein.
 7. A laminate according to claim 6 wherein said tackifier isselected from the group consisting of rosin, polyterpene resins,thermoplastic phenolic resins, hydrogenated rosin esters ofpentaerythritol, and coumarone-indene resins.
 8. A laminate according toclaim 6 wherein said adhesive contains a solvent present in an amountsufficient that said adhesive composition has a total solidsconcentration of from about 10 to about 35 percent by weight and inwhich said block polymer is a branched copolymer and said coupling agentcontains at least three reactive sites.
 9. A laminate according to claim8 wherein said solvent is an inert organic solvent selected from thegroup consisting of paraffinic hydrocarbons, cycloparaffinichydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ethers,ketones, esters, and mixtures thereof and said coupling agent is silicontetrachloride or a hexafunctional epoxidized linseed oil.
 10. A laminateaccording to claim 6 wherein (a) is a branched rubbery block copolymerand (1) is butadiene and (2) is 4-methylstyrene, 4-ethylstyrene, or4-tert-butylstyrene.
 11. A laminate according to claim 10 wherein (b) isa pentaerythritol ester of hydrogenation rosin, and there is alsopresent a solvent which is a mixture of naphtha and toluene.
 12. Alaminate according to claim 6 wherein said copolymer contains from about65 to about 85 parts by weight of said conjugated diene and from about35 to about 15 parts by weight of said styrene and saidhydrocarbyl-substituted styrene, and the amount of saidhydrocarbyl-substituted styrene, based on the total of said conjugateddiene, styrene, and hydrocarbyl-substituted styrene, is within the rangeof from about 2 to about 7 parts by weight of saidhydrocarbyl-substituted styrene per 100 parts by weight of the total ofsaid conjugated diene, styrene, and hydrocarbyl-substituted styrene. 13.An article according to claim 6 wherein at least one of the layers ismetal.
 14. An article according to claim 13 wherein the block copolymerof said adhesive contains butadiene-styrene and 4-methylstyrene,4-ethylstyrene, or 4-tert-butylstyrene.
 15. A laminate according toclaim 6 in which said block polymer contains 70 parts by weightbutadiene, 10-29 parts by weight styrene, and 1-20 parts by weight4-methylstyrene.
 16. A plurality of layers having between adjacentsurfaces thereof as a bonding material therefor an adhesive compositionwhich consists essentially of a rubbery radial block copolymer of(a) aconjugated diene containing 4 to 12 carbon atoms per molecule, (b)styrene, and (c) a hydrocarbyl-substituted styrene of the formula##STR4## wherein R is a hydrocarbyl radical containing 1 to 12 carbonatoms selected from the group consisting of alkyl, cycloalkyl, aryl,alkenyl, cycloalkenyl, and combinations thereof and n is an integerhaving a value within the range of 1 to 5, said rubbery block copolymerhaving an inherent viscosity within the range of from about 0.5 to about3 and being represented by the general formula (A--B)_(x) Z wherein A isa resinous (nonrubbery) polymer block of styrene andhydrocarbyl-substituted styrene, B is a rubbery polymer block ofconjugated diene, Z is a residue from a coupling agent, and x is greaterthan 2 and represents the number of (A--B--) polymer blocks coupledtogether, and wherein said block copolymer, based on 100 parts by weightof copolymer, contains from about 50 to about 90 parts by weight of saidconjugated diene and from about 50 to about 10 parts by weight of saidstyrene and hydrocarbyl-substituted styrene and the amount of saidhydrocarbyl-substituted styrene to the total of said conjugated diene,styrene, and hydrocarbyl-substituted styrene is within the range of fromabout 1 to about 20 parts by weight of said hydrocarbyl-substitutedstyrene per 100 parts by weight of the total of said conjugated diene,styrene, and hydrocarbyl-substituted styrene, (d) from 0.4 to 1.5 partsby weight of a tackifier selected from the group consisting of rosin,polyterpene resins, thermoplastic phenolic resins, hydrogenated rosinesters of pentaerythritol, and coumarone-indene resins per one part byweight of said block copolymer, and (e) an inert solvent selected fromthe group consisting of paraffinic hydrocarbons, cycloparaffinichydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ethers,ketones, esters, and mixtures thereof and wherein said solvent ispresent in an amount sufficient that said adhesive composition has atotal solids concentration of from about 10 to about 35 percent byweight.
 17. A plurality of layers having between adjacent surfacesthereof as a bonding material therefor an adhesive compositioncomprising a block copolymer consisting essentially of radial copolymerof a conjugated diene styrene and a hydrocarbyl-substituted styrene ofthe formula ##STR5## in which R is a hydrocarbon radical containing 1 to12 carbon atoms selected from the group consisting of alkyl, cycloalkyl,aryl, alkenyl, cycloalkenyl, and combinations thereof and n is aninteger having a value within the range of 1 to 5, said block copolymerhaving an inherent viscosity within the range of from about 0.5 to about3, said conjugated diene containing 4 to 12 carbon atoms per molecule, atackifier, and an organic liquid solvent, and wherein said blockcopolymer, based on 100 parts by weight of copolymer, contains fromabout 50 to about 90 parts by weight of said conjugated diene and fromabout 50 to about 10 parts by weight of said styrene andhydrocarbyl-substituted styrene and the amount of saidhydrocarbyl-substituted styrene to the total of said conjugated diene,styrene, and hydrocarbyl-substituted styrene is within the range of fromabout 1 to about 20 parts by weight of said hydrocarbyl-substitutedstyrene per 100 parts by weight of the total of said conjugated diene,styrene, and hydrocarbyl-substituted styrene.
 18. The laminate of claim17 in which said adhesive composition has a solids concentration withinthe range of from about 10 to about 35 weight percent of said adhesivecomposition.
 19. A plurality of layers having between adjacent surfacesthereof as a bonding material therefor an adhesive composition whichconsists essentially of(a) a branched rubbery block copolymer having aninherent viscosity within the range of from about 0.5 to about 3 of(1)at least one conjugated diene having from 4-12 carbon atoms permolecule, (2) at least one hydrocarbyl-substituted styrene of theformula ##STR6## in which R is a hydrocarbyl radical containing 1 to 12carbon atoms selected from the group consisting of alkyl, cycloalkyl,aryl, alkenyl, cycloalkenyl, and combinations thereof and n is aninteger having a value within the range of 1 to 5, and (3) styrene,wherein said block copolymer, based on 100 parts by weight of copolymer,contains from about 50 to about 90 parts by weight of said conjugateddiene and from about 50 to about 10 parts by weight of said styrene andsaid hydrocarbyl-substituted styrene, and the amount of saidhydrocarbyl-substituted styrene, based on the total of said conjugateddiene, styrene, and hydrocarbyl-substituted styrene, is within the rangeof from about 1 to about 20 parts by weight of saidhydrocarbyl-substituted styrene per 100 parts by weight of the total ofsaid conjugated diene, styrene, and hydrocarbyl-substituted styrene, andfurther wherein said rubbery block copolymer can be represented by thegeneral formula (A--B)_(x) Z wherein A is a resinous (nonrubbery)polymer block and B is a rubbery polymer block and wherein Z representsthe residue from a coupling agent which is capable of coupling two ormore (A--B--) polymer blocks together and wherein x represents thenumber of (A--B--) polymer blocks thus coupled and is greater than two,and (b) a solvent in an amount sufficient that said adhesive compositionhas a total solids concentration of from about 10 to about 35 percent byweight so that the adhesive can be easily applied to the surface of thematerial to be bonded or coated.